This invention relates to electric lamps and, more particularly, to electric lamps wherein the lamp envelope is sealed with a press seal, and an exhaust tube extends through the press seal.
One common type of incandescent electric lamp is a so-called S-8 wedge type lamp used for automobile brake light, turn signal and tail light applications. Such lamps typically include one or more filaments located within a lamp envelope. Electrical leads extend through a press seal for connection to an energy source. In addition, an exhaust tube extends through the press seal to the enclosed volume of the lamp envelope. The exhaust tube is used to fill the enclosed volume of the lamp envelope with a desired gas fill after formation of the press seal. The exhaust tube is then tipped off, or sealed, by heating the glass tube. The lamp is mounted in a plastic base that attaches to the press seal. A lamp assembly, including the lamp and the base, is inserted into a socket in the automobile or other vehicle.
Current lamps of this type have an elongated exhaust tube that extends beyond the press seal. It has been found that the current lamp configuration with an elongated exhaust tube is somewhat fragile and can fail upon incorrect insertion into the lamp socket. Recently, wedge lamp usage has shifted to automatic insertion techniques. This process has resulted in increased lamp failures upon insertion, due to off-axis insertion of the lamp assembly into the socket, allowing the press seal to pivot inside the base. The exposed exhaust tube contacts the inside wall of the plastic base and temporarily carries the insertion force load. A result of this type of loading may be a mechanical failure of the exhaust tube. The failure upon incorrect insertion may not be detected until a later time.
Wedge-type incandescent electric lamps which utilize an insulating base are disclosed, for example, in U.S. Pat. No. 4,603,278, issued Jul. 29, 1986 to Devir et al.; U.S. Pat. No. 4,752,710, issued Jun. 21, 1988 to Devir et al.; U.S. Pat. No. 4,877,992, issued Oct. 31, 1989 to Devir; U.S. Pat. No. 4,979,082, issued Dec. 18, 1990 to Devir; U.S. Pat. No. 5,008,588, issued Apr. 16, 1991 to Nakahara; U.S. Pat. No. 5,061,873, issued Oct. 29, 1991 to Belliveau; U.S. Pat. No. 5,186,669, issued Feb. 16, 1993 to Holman et al; U.S. Pat. No. 5,278,741, issued Jan. 11, 1994 to Ehrman; and U.S. Pat. No. 6,056,417 issued May 2, 2000 to Cheng. None of the prior art known to Applicants has addressed the breakage problem described above.
Accordingly, there is a need for electric lamps having press seal configurations which provide exhaust tube protection and for methods of making such electric lamps.
According to a first aspect of the invention, an electric lamp is provided. The lamp comprises a light-transmissive lamp envelope defining an enclosed volume, the lamp envelope having a seal and the seal having a recess, a light source disposed in the enclosed volume of the lamp envelope, electrical leads extending through the seal and connected to the light source, and an exhaust tube extending through the recess in the seal to the enclosed volume of the lamp envelope. The seal preferably comprises a press seal.
The exhaust tube includes an exposed portion external to the press seal. A substantial part of the exposed portion of the exhaust tube is positioned within the recess, so that the exhaust tube is at least partially shielded against breakage. The exposed portion of the exhaust tube external to the press seal may have a length that is less than the length of the press seal. The exhaust tube may have an outside diameter that is less than the thickness of the press seal for further shielding of the exhaust tube.
According to another aspect of the invention, a lamp assembly is provided. The lamp assembly comprises an electric lamp and a lamp base. The electric lamp may be configured as described above. The lamp base is secured to the press seal.
According to a further aspect of the invention, a method is provided for making an electric lamp. The method comprises the steps of providing a light-transmissive lamp envelope having an interior volume and an opening communicating with the interior volume, positioning a filament assembly and an exhaust tube in the opening, heating the lamp envelope at least in the region of the opening, forming the lamp envelope into a press seal such that electrical leads of the filament assembly and the exhaust tube extend through the press seal into the interior volume of the lamp envelope, and pushing the exhaust tube toward the interior volume of the lamp envelope with the lamp envelope heated to form a recess in the press seal where the exhaust tube extends into the lamp envelope.